网络外键引用 网络释义 1. 外键引用 引用键,referenced... ... ) referenced key 引用键 )foreign key reference外键引用) critical reference 关键引用 ... www.dictall.com|基于 1 个网页 例句
reference_option共有五种:CASCADE、SET NULL、RESTRICT、NO ACTION、SET DEFAULT。接下来分别说明它们的意义。 CASCADE:级联操作。即当被参照记录被删除或更新时外键值也删除或更新,写在on delete后面就是级联删除,写在on update后面就是级联更新。例如在上面的例子中,如果表”借书“定义了表约束FOREIGN KEY 借书证号...
百度试题 结果1 题目下列能够设定外键约束的关键词是( )? FOREIGN KEY... REFERENCEPRIMARY KEYUNIQUECHECK 相关知识点: 试题来源: 解析 FOREIGN KEY... REFERENCE 反馈 收藏
A Foreign Key Reference defines the necessary information needed to reference an entity in a certain table. You need to set up this control table if you need to validate a foreign key value against a corresponding table. For example, if a schema element is associated with an FK ...
一、命令行 首先FOREIGN_KEY_CHECKS方法的作用是用来启动和关闭外键约束的方法。 二、外键约束 即数据库中两个数据表之间的某个列建立的一种联系。MySQL通过外键约束的引入,可以使得数据表中的数据完整性更强,也更符合显示情况。 例如: 有两张表,一张表是学生表,存储了
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FOREIGN KEY (suno) REFERENCE subject)//从表subject中引入参照外键su_no,以确保本表与表subject的关联与同步 (2)基本表的删除:用以从数据库中删除一个基本表及其全部内容,其语句格式为: DROP TABLE[<数据库名>.]表名 例如:将上面建立的表都删除
百度试题 题目下列能够设定外键约束的关键词是( )A.PRIMARY KEYB.FOREIGN KEY... REFERENCEC.CHECKD.UNIQUE 相关知识点: 试题来源: 解析 B 反馈 收藏
On reference creation, Database Designer for MySQL performs the following actions: 1. Creates new column(s) in the referencing table, their parameters (name, data type) will be copied from the primary key constraint of the referenced table. If the referencing table already has column(s) analog...
命令格式：[CONSTRAINT [symbol]] FOREIGN KEY[index_name] (col_name, …)REFERENCES tbl_name (col_name,…)[ON DELETE reference_option][ON UPDATE reference_option]reference_option:RESTRICT | CASCADE | SET NULL | NO ACTION | SET DEFAULT 以上是完整的官方命令格式，看着都晕呀。[CONSTRAINT <外键名...